Typically, plasma reactors use a radio frequency (RF) power source with a constant average power or voltage to excite a plasma in a vacuum chamber. Plasma reactors in which the RF power source is coupled to the process chamber inductively, also referred to as inductively coupled plasma (ICP) reactors, are widely used, for example, in silicon and metal etch applications. Most of these reactors have an additional RF generator coupled proximate the substrate in which plasma is coupled capacitively to the chamber. This additional RF generator is often referred to as a bias RF generator.
In some ICP reactors, the source RF generator and the bias RF generator may operate using a common exciter to force both generators to generate the same single frequency. Unfortunately, however, the inventors have observed that phase misalignment of the signals produced by the respective generators may cause problems during processing. For example, although current commercial ICP reactors try to align both source and bias signals to have zero phase difference, the actual phase difference is rarely, if ever, zero. In addition, variations in the actual phase between source and bias generators naturally exist, causing chamber-to-chamber variation in their respective phase differences. Such differences in phase within a chamber and between chambers affects the ability to provide consistent processing amongst otherwise identical chambers.
Therefore, the inventors have provided improved inductively coupled plasma reactors and methods of use as described herein.